Silver Spirit and Bentley Mulsanne 1987-1989 Model Years

20,000-Series Supplement

ABS Braking System

Although This Section was Prepared for 30,000-Series SZ Vehicles, it Also Generally Applies to 20,000-series SZ Vehicles

rht 22 September 2008

Workbook

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ar' FOREWORD

Th s workbook is for usewith the Rols.Royce l\4asteriech Video Programme'Antl-lock Brakes and Hydraulic System Changes fJom VIN 20001'

It contains additional inlormalion about the design and working principles oftheAntilock Brak ng System and Hydrau cs Systems litted to Bol s Royce MoiorCarsfrom VIN 20001

CONTENTS

lntroduction

Braking TheoryFricUonTyrelRoad Braking ForceComparison belween Norrnal andAnli-lock Braking in a Skid Silualion

Modulator Controlled Anti-lock Braking SystemPrinciples oI Operalion

ComponenlsOperat on

Nudber 1 Hydraulic SystemComponenlsDescript on

Number 2 Hydraulic SystemComponenlsDescript on

Hydraulic Modulator AssemblyComponenlsHydrau ic Connect onsOperation

Wheel Sensors and Phonic WheelsFronl Hub ComponentsRear Hub CornponentsOperationOutputSignal

Electronic Conlrol UnitComponentsOperationOperating Phases

Hydraulic System ReservolrsComponentsFeaiures

Heighl Control ValveComponentsOperation

Height Control SystemPrinciples of Operation

ComponentsOperation

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lntroduclion

Components

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567

AccumulatorsBrake d stribution valveHydraullc modu atorFro nt wheel cal persRear wheel caLipers

E ectron ccoftro un t

Operation

An Antr-lock Brak ng Sysiem is a braking systemwhich ncorporates a controllunct on 10 prevenlthewheels lock ng dur ng brak ng with resu tani oss ofbraking etticiency and d rectiona stab lty.

The Antr-lock Brak ng System frtled to Rolls Boyceand Bent ey IVotor Cars lncorporates awheelsensorsystem, an electronlc control un t and e ectr ca lyoperated valves in the brak fg c rcu 1s.

The wheelsensor system continla ly rnonilors thestatus 01 each individual whee d!r ing brak ng.When a whee is aboutto ock, the electron ccontrolu nit operates valves in the brak ng circuits to controthe brake calper pressure to obta n oplimum0rakrng.

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Braking Theory

Friction

Friclion is the resrstance to movemenlwhichoccurs when one object slides over another

The frct on force (F)is equa to thewe ght 0ftheobject (w) tinres the coeif cient of frict on (!).Frcliona force does nol depend on the contactaTea.

Coeflicient ol f ricllon

The coelf cient oifrict on changes wth the speed atwh ch one object sldes over another.

Ths h ghestva ue oicoefl ic ent occurs when theobjecl isjusiaboutlo move and is reJerred lo as iheslalic coetlicjent ot Iriclion (A).

The lowest value o{ coellicient occurs when lheob,e.l s nov rg a^d s rerefled lo as lhp dy_ariacoefl icient of Ir ict ion (B).

The static coeti cienl ol ir ct on s h gherthan thedynam c coetl ic enlotlr icl ion.

lhe v.rlue ol lhe coellrrenl ol hiclion changesaccording to lhesliding surlace bet\iveen theobjects. For exampe, the statc coelJic ents oftriclion befur'een a road tyrear]d llre road suriacevary trorn 1 00 lor dry concrde, (A), 1o 0.95 for wetconcfete, (B)

ll theroad is covered In snow,lhe coetlicienl ollriction lalls to 0.20. (C), whilelhe coet{icienl oltriction lor a tyre on ace ls 0.10, (D).

Tyre/road braking torce

The maximum braking lorce beiweenlhe road andwheelis limited by lwo Jactors, lhe vehicle weighland the coefficient ol lriclion between the road and

A ro l ing wheel s slal icfr ict ion. A locked ors rdingwheel is a dynam clrct on si luat on.

Thereiore, d!r ng brakrng it is most importantthatlhewheeldoes nol lock. It il does, the coetlicienlol tiction willbe reduced, increasang thewheellocking etlect and reducinglhe maximum braking

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Lr:aimr l Wheelsl ip

A Straightlne brakingB Corner ng forc-.C Combined braking and corner ng forceD Anti-lock brake operating range

A certain amount ot slip between the tyre and road rsnecessary fora roadwheelto rolland steeretlioently Anli.lock brakes operate eflicienlly ina8"/" - 307" range otwheelslip.

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Comparison between 'Normal' and 'Anti-lock'bmking In a skid si tuat ion

Graph A - Brake Force Vs TlmeGraph B- Boad Speed VsTime

1. Norma Braking System

When the brakes are app ied, the brake lorcebetween lhe road and whee ncreases rapidly (1)up to the pointatwhich lhewheel locks As thisoccurs,lhe maximum braking force available atthetyre road interlace tor braking is reduced by thelransition trom static to dynamic lriction (2). As longas lhe samebraking conditions prevail,lhe wheelwi l lconl inuelo skid (3)unt i l i l l inal ly stops Juslbelore lhe carslops, the speed reduces lo lhepoinlwhere lhe hiclion relurns lo a slaticcondilionand the brakelorce increases momenlarily (4). Assoon asthe carstops, the brakes are re eased (5)

2 Ant ock Braking System

Whenthe brakes are app ed,the brakelorcebelween the road and whee ncreases rap dly (1)Lpto L!e por_lalwh Li- heABSsr'srer se^sesttsatthewheelisaboutlolock As this occ!rs. the antilock braking system lirsl holds the braking lorceconslant (2)while moniloring the change inwheeldeceleration- lf the ABS system iudges lhat thewheel will slill lock, itreducesthe brakelorcemomenbri ly(3)unti l thewheel isrol l ingagaan. TheABSsyslemthen restores maximum brakang lorce(4)unli l i lsensesthalwheel lochwil lhappenagainwhen il holdslhe brakepressure. The'HoldBelease - Fleslore cycle (5) is repeated lhroughouithe brake applcat on ensuring thatopt mum brakingis ach eved unu ihe car stops and the brakes arereleased (6)

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Modulator Valve Controlled Anti-lockBraking Circuit - Principles of Operation

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Components

A AccumllatorB Braked stribulion valveC Brakecallper) Wheelspeed sensor

E E ectron c contro uniiF l\,4odu atorvalveG Reservoir

Each ind vidua Anti lock Braking Circuil comprlses anorrnaipower braking system of an accumulator, A,brake distributoa valve, B, and brake calper, C,which incorporates an addilional electr cal ycontrol ed modulator valve, F.

The modu atorvave aso has an hydraulicconnectiontolhe reservo r, G. l tconia ns avalvesystem which can controlthe f low ofrnineraloi l tothe brake ca iper.

The operal ion oithe modulatorva ve s coniroled byan electronic controlunit, E, which s supplied wrthwhee speed nlormation s gnas by the wheelspeedsensor, D,

Whenever braking occurs, the e ectron ccontrolunitmonitors the whee speed s gnalslor each wheeland determrnesthe car speed, ind vdualwheelspeed,lnd v d uai wheel deceleration and ndrvidualwheelsl ip.

lflhe e ectron ic conlrol u nit receives signalsindicating heavy wheel deceleration llke yto causewheellock, t sends electr cal signals to themodulator valve to coniro the brakrng pressure tothe appropriate wheel.

Th s bfak ng control is ach eved using three modes,Normai, Hold and Release operatlng ata highlrequency between 4to 10 times per seconddependant on road condilions.

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Operation

1. Normal mode

ln ther]orma mode, the modulator valve is in anopen posit on n which t has no etfecl on ihe brakehydra!lic pressure behrr'een the brake distr butionvalve and whee caliper.

When the modu atorvalve is in th s postion,lhebrakes operate n the norma way.

2. Hold mode

In the hold mode the electron c conlro !n t causesthe modu atorvalveio c ose the hydraulc clrcu tbetlveen ihe brake d slribut o|l valve and thewheelca per

This act on elfectvely sea s the brake circu Ibet\^/een lhe modLllatorvalve and whee ca iperprevent ng anylLrdher ncrease in brake ca iperpressLre.

3. Release mode

inthere ease mode, the electron ic co ntro unitcauses the modulator va veto open a return crrcu tbeh/r'een ihe brake caliper and reservoir.

Th s alows some oJthe nr nera ol nthewl ' reecalperto return tothe reservorr, effective y reduc ngIne ca peTpTessuTe

Al the samel me, the rnodLrlaiorkeeps the hydraulcsupp y trom the brake distribut on vaive c osedpreventLng any increase n the ca per pressure unlithe norma mode s selected.

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Number 'l Hydraulic System

Componentsl

lvlodulalor (antFlocking brakes)Front hydrau llc pu mpFront hydraulic accumulatorHydraulic mineral oil reservoirHydra!lic pressure warning switchUpperd str ibui ionvalveDeceleration conscious pressurelimiting valve ('G' valve)PriorityvalveFiterblock assemb yMinimum pressurevalveSeepage return hoseLevellingvalveBleed poini ' Suspension strutsRear brake caliper (lour cylinder)Rear brake caliper bleed pointReslriclorGas spr n9 and S!spension strul

Descdption

NumberOne Hydraulic System complises lwocircultsied by the fronl p!mpand lront accumulator:

The Roar Braking CircuitThe Height Conlrol Circuit

Rear braking clicuit

Rear braking is achieved using two parallel circuilssupplled by the same brake distr ibut on vave andmodulalor valve which op€rate the conventionai fourcylinder rear u,heel calipers.

One olihe c rcuits incorporateslhe reposiiioned Gvalveto maintair optimum pertormance ofthe rearoraKes.

Height controlcircui l

The height control circuit tealures a priority valve,minimum pressure valve and a single heightconlrolvalve 1o operale the co nventio nal mineral oil gasspnng and suspension strut.

Relocation ol lhe height controlvalve and a newactuation system (see page 17)ensurethallheheightcontro systern reacls onlyto addit ion orsubtraction of vehicle weight.

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Number 2 Hydraulic System

Components

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[,4odu ator (anti ocking brakes)Frontleading brake ca iper(twin cyllndedRearhydrau ic accumu atorRear hydrau icpumpFronttrai ing brake cal per(twin cylinder)Hydrau ic mineral oil reservoirHydraulic pressure warning swltchLowerdlstribulion valve

Description

N!mberTwo Hydraulic System which is fed byiherear pump and rear accum!lator, provdesfrontwheeL braking only through conventional tw ncy inder eadlng andtra Ing brake calpers.

The brake system is divided nto two circuils atthemodu ator valve where individual modulators controlthe operation olthe front leftwheelbrakes and lrontright whee brakes.

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Hydraulic Modulalor Assembty li: )

Components

I Modulaior assembly2 Eleclr icalplug3 Modulalorrelay4 Flexible mountings

The hydraulic modulator valve assembly islocaled intheenginecompartment. immediatelyintrontoltheletl-hand fronl spring pot.

The assembly containsthree e ectrica ly operaledso eno d va veswhich provide separate ant ockbrake conlroltorthe leJt hand front brake circ! i l , theright hand lrontbrake c rc!itand a corrlmon rearbrake circuit.

The modu atorassembly s located bythree l lexible ,moLrnls, one on the nboard side o{ lhe modulalor,one on the outboard s de and one ai ihe rear ol lhemodulalor.

The modulatorrelay rs specially builllo much higherlolerances and musl nol be subsliluled by aslandard relay.

Hydraulic connections

I To rear brake calapers,Blue pipe, PortA.

2 To righl-hand lronlcahpers,Ivlauve p pe, Port R

3 To eft hand frontcallpers,[/auve pipe, Poa( L

4 l_o ollboard reservoir lsystem 2),Whilepipe, PortT.

5 To lnboard reservo r (System 1),B ack pipe, PorlTT

6 From Lrpper brake distribution vave,Blue pipe

7 From lower brake dislribution valve.N4auvepipe.

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Components

10 13 11

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IVlodulalorva veBrake d stribut on valveBrake ca iperReservo rnLet poirfrom brake distribution valvelnletva ve (normal y open)Out et porlto brake ca perOut et port to reservoirOut et valve (normally closed)Eleclrica so enoidSo enoid p ungerReturn spr ngVavespnngs

Operation

1 Normal mode

In the normalposit ion, no currenlf owsthrough theso enod The ret!rn spring pushesthepungertothe rght. The oLrtetva ve s he d closed andtheIn el valve is he d open. {Vl nera oi l from the brakedistr butron va ve can f ow to and trom the brakeca iper w thout any eftect.

2 Hold mode

In the ho d posit ion, elecir calcurrentpass ngthrough the so enoid causes the plunger to move lothe elt This acl ion closesthe if lelvalve. The out etva ve fema ns c osed. Brake pressure bebreenthemodu alorand ca iper is he d constanl.

3 Release mode

In the re ease posion, ncreased electricai cu rrenipass ng through the soleno dcauseslheplungerlomove furthertoihe 1e11. Th s action opensthe outletva ve. The in etva ve reflra nsc osed. Brakepressure between the modulator and callper s'eo. .od oy 1 i ' lp a or 'ar- rng ro lhe re>e lo i

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Wheel Sensors and Phonic Wheels a. l

Fronl hub component" {i..1

1 Froni hub carr er2 Front hub3 Front hub phon cwheel4 Front wh eel sensor5 Sensor slgna cable

TheABS phonicwhee ls aseparate cor.ponentwhich s pressed ontothefronl hub.

The ABS system senses nd v dualwheelspeedus ng an r]ducivesensorand a rotal ing toothed

Thephonicwhee forrns pair oithe whee hub.Thesensor s secu rely localed n the hubcarrier napos t on where t l ' reteeth on the phonicwheelpass lIne sensoriace.

The d stance betlveen the sensorface and the1ee1h ofthe phonicwheel s0.25 l.52mrn(0.0100.060 n.).Th s gap is notadluslable.

The outpul signa cabe frorn the sensor is nlegrawihthesensoral thesensorendand seeclrcaly5n eloed A p .g rg d. ldched 'o | ts. o lh-r e_c o l l_.cab e to fac ltate sensor fep acenrenl.

Bear hub componenls

1 Fear hub carr er2 Rear hub3 Rearhubphonrcwheel4 Rearwheelsensor5 Sensorsgnalcable

TheABS phonicwheel s rnachined ntothe rearhub

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Componenls

I Permanentmagnet2 Inductivecoil3 Phonic (loothed) wheel4 Shielded s ignal cable 10 the elecifon ic conrroi

unit.

Operation

As each tooth on the lhe phonic wheel passes thelace of the sensor, it changeslhe magnelictietdsu"o-n0rng the perTa.lent Tagnet. The change t-TagnelC le d r_ouces eleclr calc-re.I ir r" leinductrve coilwhich is connected tothe electronrccontrolunil.

Output signal

The output signal from the sensor s s nusoidal. Thefrequency ol the slgnalchanges with and lsproportonal to wheel speed_

Wheelspeed 'B' is twice wheet speed'A,.

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Electronic Control Unit

Componenls

I Elechoniccontrolunil2 Wiring harness 35 pin plug3 35 pin plug locating latch

The eleclronic conlrolunil is located in the luggagecomparlm€nl ll is mounted onthe lefl handsiderearwheelarch behind thetr m panel. Conneclionsare madethfo!qh a 35 pin plug connectorwhlch satched to lhe control !rnit for secur ty.

Operation

Whenever braking occurs, the eleclronic control unitcontinualy monitorslhewhee speed srgnalsirom alfou' wheer sensors f o-n t\ese s'9nals. r lcon_o-lestheroad speed, individualwheel speed, and lheacceleration, deceleralion and wheel slip of eachindividualwheel.

From lhe signals it receives,lhe electroniccontrolunil can determine whetheror not the decelerationol a wheelorwheels is likely to resull in wheel lock

In lheeventol heavy deceleration occurring likelytocause wheel lock, lhe eleclron ic control u nit sendssignals lo the appropriale modulating valve to adjusllhe braking pressure to lhe wheel, by holding,reducing or increasinglhe brake pressure asappropriate lo lhe wheel deceleration stalus Theellect ot each conlrolaclion is monilored by lheelectronic conlrolunit irom the change in the signalsernitted by the wheel sensors.

The elecl.o-tc ( o-.,ol ,r, ic p.oo.a- Teo wiln d se 'testsequencewh ch checksthe rntegrity oitheABS electrical syslern each time the eng ne isstarted. I i tdetects afaultduring th s test iwlautomat caly swtch tse f oifand causeiheANT LOCK warning lghtto luminate.

When this occurslhe modulators remain larl sate rnthe normalposition allowing the braking system tofunction normally-

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an operating phases

fhe actlon ofthe eleciron c conlrolun t (ECU)canbe considered as three phases, norrna, hold andre ease, corresponding lot l ' rethree rnodulatorva vepos t ons.

Normal phase

1 The wheel is dece erat ng.2 Brake presslrre s increasing.3 The ECU deterrn nes thatwheellock is I kely

IO OCCUT.

Hold phase

3 The ECUdeternr nesthatwheel ockisl iketyIO OCCUr

4 The ECU swtches the modu alorvalve to. " Hod posit ion.

5 Brake pressure s held constant.6 The ECU determines that the wheel

dece erat on is st I ikelyto causewheellock

Release phase

6 The ECU delerm nesthatthewheeldece eraton is st i l ikelyto cause wheel lock

7 The ECU swlches the modLr atorvalve to'Release positlon.

I Brake pressLre is feducedI The whee acceleraies aga n10 The ECU determinesihatthewheel snot

being braked etf ciently

Normal phase

10 The ECU determines thal the wheel snotbeing braked eff ciently.

11 The ECU switches the modLrlatorva veto'Normal' positioll.

'2 Bra(F o essu.e rn, rpr .ps dgai.- 1 Tf,p wL eeloece arates aga r14 The'Ho d'cycle repeats

The controlsequence can be repeated 4 io 10trmes persecond to provrde ma( murn braking eI{ect

' , fof the preva |ng condt ions.

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Hydraulic Mineral Oil Reservoirs

Components

1 Numberonesystem reservo r2 Number lwo syslem reservoir3 Mult i - ingua warn ng panel4 Wire and seal

NLrmberone Teservo rsupples mineralo l torthe rearbrakes and heighl contro

Numbert\roreservoirsupplesminera o for lhelront brakes only.

Reservoir components

2 Beseruo rtop3 Outei to hydrau ic pump4 F l ter5 Comb ned reservorr evel ndicator and evel

6 Levelsight g ass7 Level nd catortloal mechan smB Fl ingpont

Features

The new lrydraLr c reseruo rs are rnanulactured frorfan opaque rnater al A lconnecl lons are madethrough the top ol lhe reseruo rtom n rnise leakageLeve ndicat ion s achleved by adouble f oatsystemwh ch operales avisua eve nd cator. The levelindlcai on system incorporates a reed swtch wh chcontrols lhe operat ion ofthe ow minera o lwarningl ight One of the f loats in the syslem a lows lor nat!ralchanges n the reservo r levels caused bythecharglng and discharging of the heighl controlstruts.thereby avoiding inaccuraie evelind cations causedbyveh ce load condit ions.

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Height Control Valve

Components

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He ghtconlro va veOperating lever

Torsion barCampng polntRear anti-rol bar

Operalion

The he ghtconlro system s operated by a singleheighl control valve mounted on the left-handsideot lhe rear cross member Actuation is achieved by atorsron barwhrch is clamped to the centre ot lhe rearant roi bar.

The new conliguration ol the height mnlrolvalveand its operating mechanism negates the etlecl olbody fol on the heghl coniro system, ensuringthallhe syslem ls atiected by changes n veh cleweight

A - Cornering

When lhe car corners, body follcauses an upwarddelleclion olone end of theanli rollbarand acorresponding equal downward de{leclion ol the

Al lhe centre oJ the anti-rollbar, no movemenliakesplaceas thedetleclion ol the endsol theanti rollbaris taken up byt\rist n ihe cenlre portion oithe bar.As a reslr t, th stwisting actroll olthe anii-rol barcaused by body rolldLrring cornering has no elfecton lhe height conlrol syslem.

B - Height control

When vleight is addedto or removed fromihe car,bolhends ollheanli rollbar dellect in thesamed rection, upwardswhen weight is added,downwardswhen we ght is removed.

ln lh|s case, the centre ol the anli-rollbar rotatescausing movemenl in the torsion bar connected tothe he ght controlvalve. Th s aci on is transmittedtoa everwhich compresses or expandsthe he ghtcontrol vaive accord ing ly.

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Height Control SystemOperation

Components

Principles ot { :

123456

Height controlvalveRear sLrspens on strutGas springD aphragmCornpressed gas

Operation

Normal suspension movement

When the wheel hits a bLrnrp in the road,lhe pislon sforced upwards nto the strut. Minera oi in the strut islorced into the gas spring. cornpress ng the gasbehind the d aphragm.

Conversely, when the wheel h ts a pot hole. t irep ston s torced downwards bythe expans on ol thegas

Heighl control

As weight is added to lhe car t causes compress onolthesuspens on.This reacton s lransrni i ted lo theherg ht conlrol va ve wh ch restores the car lo tscorrect heighl by increas ng lhevo ume ol m neraloin the strut The increased vo ume torces lhe p stonrod out olthe strut.

Converse y, asweighl s removedirom the car,theresu iant expansron of the slspens on causes theheghtconlolvavetoalowminera oi toreturnlromthe slruttothe reservoir The piston moves upwardsreducngthe carhe ghiunt i l thevavecoses.

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